1. Field of the Invention
This invention relates generally to integrated circuits and more particularly to integrated circuit packaging assemblies.
2. Prior Art
Wire bonding is the technique generally used for electrically connecting an integrated-circuit die to the leads of a leadframe. Each bonding wire connects a bonding pad on the integrated-circuit die to a bonding finger on the leadframe. The lengths of bonding wires have been increasing due to several technological developments: smaller die sizes, larger die-attach paddle areas, and the requirement for minimum lead spacing while an increased number of leads are required. Use of a smaller die with the same size leadframe requires a longer bonding wire. The increased number of bonding pads and the requirement for minimum lead spacing causes the bonding fingers of the leadframe to be farther away from a die positioned to the center of the die-attach paddle of a leadframe.
In general, a bonding wire having a length greater than 150 mils has reliability problems in many package types. A gold thermosonic-bonded bonding wire with a length of 175 mils has excess wire sag which may causes shorting between wires. Moreover, during the plastic molding process, which encapsulates the integrated-circuit die and its related elements with a plastic molding compound, so called wire wash effects occur due to the washing, or sweeping action of the molding compound. This results in physical breakage of the bonding wires and also causes electrical shorts to occur between the long, thin bonding wires with lengths greater than 100 mils.
Various types of coatings have been used to avoid the shorting and wirewash problems associated with using long, thin bonding wires. However, use of these coatings require either extensive process modifications or they have questionable reliability. One bonding technique which avoids the use of long bonding wires is the tape-automated bonding (TAB) technique, such as described in U.S. Pat. Nos. 3,689,991 and 3,544,857, which disclose use of a metallized polyimide TAB tape to bridge the gap between a bonding pad on a die and the bonding finger. The additional financial cost and the process modifications required for use of the TAB technique have kept conventional bonding-wire techniques commercially viable.
Consequently, a need exists for an economical, easily implemented technique for bridging gaps greater than 175 mils between the bonding pads of an integrated-circuit and the associated bonding fingers of a leadframe.